Superconducting accelerating tube comprised of half-cells connected by ring shaped elements

ABSTRACT

A superconducting accelerating tube which is constructed by welding and connecting a plurality of half cells (11) formed of superconductor material in a dish form having a substantially constant wall thickness of the material, and having a small-diameter portion (11a) and a large-diameter portion (11b) and in which the shell diameter periodically varies. The half cells (11) are welded together via ring-shaped connecting members (12) formed of superconducting material and disposed between the small-diameter portions (11a), and the half cell (11) and connecting member (12) are formed of Nb.

TECHNICAL FIELD

This invention relates to a microwave charged particle accelerating tubeformed of a superconductor.

BACKGROUND ART

In an accelerator using a high frequency electric field to acceleratecharged particles, an accelerating tube is used as a device forgenerating the high-frequency accelerating electric field. Such anaccelerating tube is preferable to accelerate the charged particles to ahigher energy level while using less microwave power. It is said thatthe accelerating tube formed of superconductor material may serve theabove purpose since the high-Frequency resistance on the tube wallthereof is small.

The conventional superconducting accelerating tube (FIG. 9) isconstructed by working a hollow disk of superconducting material such asNb into a half cell 1 in a dish form having a substantially constantthickness and having a small-diameter portion 2 and a large-diameterportion 3 which are open at the end portion thereof as shown in FIGS. 7and 8 and then welding the half cells together into a tubular form. Thatis, the superconducting accelerating tube is constructed by arranging aplurality of half cells 1 with the small-diameter portion 2 andlarge-diameter portion 3 of each half cell set to face thesmall-diameter portion 2 and large-diameter portion 3 of adjacent halfcells as shown in FIG. 9 and then respectively welding thesmall-diameter portion 2 and large-diameter portion 3 of each half cellto the small-diameter portion 2 and large-diameter portion 3 theadjacent half cells by use of an electron beam, for example, so as toconnect the half cells.

With the above superconducting accelerating tube, it is impossible for awelding machine to approach a portion near the small-diameter portion 2having the smallest diameter from the inside thereof since the diameterthereof is small. Therefore, when a plurality of half cells 1 areconnected together by welding, it is required to weld the small-diameterportions 2 from the external surface side. However, since the wallthickness of the material of the half cell 1 is small, weld beads mayeasily occur on the internal surface side when the small-diameterportions 2 are welded together from the external surface side.

Since the electric field is strong near the small-diameter portion 2 ofthe superconducting accelerating tube, discharge may occur if the weldbeads are left behind on the internal surface side. This is notpreferable. Therefore, in the superconducting accelerating tube, smoothabrasion of the inner portion of the small-diameter portion 2, or thelike, must be carried out after a plurality of half cells 1 are weldedtogether.

Therefore, the half cell 1 is required to have a wall thickness (1 mm)larger than a certain value in order to make it possible to easilyeffect the welding operation, take a sufficiently large abrading margin,etc. after the welding operation, and have a sufficiently large strengthwhich may prevent occurrence of deformation during the abrading process.

The characteristic of the superconducting accelerating tube largelydepends on the heat conductivity thereof, and it is necessary to attainhigh heat conductivity and enhance thee cooling efficiency in order tostore a large amount of energy.

That is, the superconductor has a high-frequency resistance so that alarge amount of heat will be generated on the surface of thesuperconductor particularly in an electromagnetic resonator such as anaccelerating Lube for storing a large amount of energy. Therefore,unless the heat is sufficiently quickly dissipated, the temperature ofthe superconductor rises and the superconductivity thereof will bedestroyed before long.

Since the high-frequency excitation mode ordinarily used in theaccelerating tube is TM₀₁₀, the largest current will flow in a portionnear the large-diameter portion 3 having the largest diameter and thesmallest electric field. In contrast, in the small-diameter portion 2having the smallest diameter, the electric field is high but the currentis small. Since a large amount of heat may be generated in thelarge-diameter portion 3 in which a large current flows, it is necessaryto enhance the cooling efficiency of the large-diameter portion 3.

As described above, in order to store a large amount of energy, it isnecessary to enhance the heat conductivity of the superconductingaccelerating tube and thus enhance the cooling efficiency. In order toattain this, it is preferable to enhance the cooling efficiency byreducing the wall thickness of the material of the superconductingaccelerating tube.

However, in a case where the superconducting accelerating tube isconstructed by welding as in the prior art, the possible degree ofreduction of the wall thickness is limited.

As one of the prior art methods, there is used a method of enhancing theheat conductivity by enhancing the purity of the superconductor materialsuch as Nb which constitutes the half cell 1 to increase the residualresistance ratio RRR. However, the method off increasing the RRR alsohas a limitation and it cannot be said that the present method issufficiently good.

Further, as another prior art method, a half cell obtained by plating asuperconductor material on a good heat conductor such as copper oraluminum has been developed. However, since the thickness of thesuperconductor material of the half cell is small, the platedsuperconductors cannot be welded together and therefore it is necessaryto plate the superconductor on the joined portion after the half cellsare joined.

This invention has been made in view of the above, and an object thereofis to provide a superconducting accelerating tube in which the wallthickness can be reduced to enhance the cooling efficiency and the halfcells can be easily welded together.

SUMMARY OF THE INVENTION

In order to attain the above object, according to this invention, asuperconducting accelerating tube is constructed by welding. Theinvention comprises connecting a plurality of half cells formed ofsuperconductor material in a dish form having a substantially constantthickness and having a small-diameter portion and a large-diameterportion and in which the shell diameter periodically varies. The halfcells are welded together via ring-shaped connecting members formed ofsuperconducting material and disposed between the small-diameterportions.

The superconducting accelerating tube of this invention is constructedin a tubular form by disposing connecting members between the half cellsand welding a plurality of dish-shaped half cells which are each formedof superconductor material and have small- and large-diameter portionson both sides.

With the above construction, the inner diameter of the small-diameterportion of the half cell is increased by an amount: corresponding to theconnecting member, and the connecting member, and the half cell can bewelded together from the internal side. Therefore, the welded surfacecan be made smooth and the post-treatment such as the abrading operationis not necessary.

Further, the half cell and connecting member utilize niobium (Nb) as asuperconducting material.

Preferably, the half cell and connecting member have a layer of Nb₃ Snor NbN formed on the internal surface of Nb. When such a layer isformed, it is possible that a higher accelerating electric field can beattained since the critical magnetic field is enhanced.

For example, when a layer of Nb₃ Sn is formed on the inner surface ofthe half cell, Sn is plated on the inner surface of the half cell formedof Nb and is then subjected to a thermal oxidation process so as to forma layer of Nb₃ Sn.

The wall thickness of the superconducting accelerating tube is limitedby the wall thickness oil the small-diameter portion off the half cell,but this invention, the wall thickness of the small-diameter portion canbe reduced by providing the connecting member. Therefore, the wallthickness of the large-diameter portion in which the cooling efficiencyis most severely required can be reduced, making it possible to enhancethe cooling efficiency.

In this case, the wall thickness (mm) of the half cell constituting thesuperconducting accelerating tube is preferably set to be equal to ormore than 1/800 of the inner diameter (mm) of the large-diameterportion, and more preferably, it is set to be equal to or more than 0.1mm and equal to or less than 1 mm.

Generally, in a superconducting accelerating tube, a relationapproximately expressed by the following equation (1) is set up betweenthe resonant frequency f (GHz) and the diameter d (mm) of alarge-diameter portion corresponding to the large-diameter portion ofthe half cell.

    f×d=250                                              (1)

However, in the superconducting accelerating tube of this invention, itis difficult to work the connecting member so as to make the thicknessthereof equal to or less than 5 mm. For this reason, if the wallthickness of the half cell is set to be equal to or less than 0.1 mmwhen a superconducting accelerating tube in which the diameter of thelarge-diameter portion is equal to or less than 80 mm is used, theweight of the connecting member cannot be supported and proper weldingcannot be attained. On the other hand, when the wall thickness of thehalf cell has exceeded 1 mm, the heat conductivity is lowered and thecooling efficiency of the superconducting accelerating tube is reduced,and this is not preferable.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross sectional front view of a superconducting acceleratingtube of this invention;

FIG. 2 is a left side view of the superconducting accelerating tubeshown in FIG. 1;

FIGS. 3 to 5 are cross sectional front views showing a processmanufacturing a superconducting accelerating tube of this invention;

FIG. 6 is an enlarged cross sectional view of a portion of the tube ofFIG. 5, showing a layer of Nb₃ Sn or NbN on an inner surface of a halfcell;

FIG. 7 is a cross sectional front view of a half cell used in theconventional superconducting accelerating tube;

FIG. 8 is a left side view of the half cell shown in FIG. 7; and

FIG. 9 is a cross sectional front view showing a superconductingaccelerating tube constructed by welding and connecting a plurality ofhalf cells shown in FIGS. 7 and 8.

DETAILED DESCRIPTION

There will now be described an embodiment of this invention withreference to FIGS. 1 to 6. In all of the drawing Figures, the samereference numerals designate the same respective elements.

A superconducting accelerating tube 10 is formed by welding a pluralityof half cells 11 into a tubular form whose shell diameter periodicallyvaries as shown in FIGS. 1 and 2 with connecting members 12 disposedbetween the half cells 11.

The half cell 11 is formed by subjecting a hollow disk formed of Nb to adrawing process, for example, so as to form the disk into a dish-shapedmember having a small-diameter portion 11a (see FIG. 1) and alarge-diameter portion 11b which are open at the respective end portionsand having a substantially constant wall thickness as shown in timedrawing.

The connecting member 12 is a ring-shaped member formed of Nb and, asshown in FIGS. 1-3, has stepped portions 12a (FIGS. 1, 2 and 3) whichare formed on the outer periphery thereof to abut against the frontportions off the small-diameter portions 11a (FIGS. 1 and 3) of the halfcells 11. The connecting member 12 is used as a small diameter portionof the accelerating tube 10 when the lair cells 11 are welded togetherto form the superconducting accelerating tube 10.

The superconducting accelerating tube 10 is manufactured as follows.

First, as shown in FIG. 3, the connecting members 12 are disposedbetween the small -diameter portions 11a of the half cells 11.

Next, as shown in FIG. 4, the front end of the small-diameter portion11a of each of the half cell 11 is abutted against the stepped portion12a of a corresponding one of the connecting members 12, and thesmall-diameter portion 11a is welded to the connecting member 12 fromthe inner surface side of a portion beside the large-diameter portion11b (see also FIG. 3) so as to form a superconducting accelerating tubeunit.

Next, as shown in FIG. 5, two superconducting accelerating tube unitsshown in FIG. 4 were set with the large-diameter portions 11b of thehalf cells 11 facing each other and then welded together. Elements 11a,12 and 12a, as seen in FIG. 5, are the same as shown in FIGS. 1-4.

Likewise, a plurality of the superconducting accelerating tube unitswere welded and connected together in the same manner to form thesuperconducting accelerating tube 10 shown in FIG. 1.

In this case, since the diameter of the small-diameter portion 11a ofthe half cell 11 was increased by an amount corresponding to theconnecting member 12, the half cell 11 and the connecting member 12could be easily welded together from the internal side and a smoothwelded surface could be obtained. Further, since the connecting member12 was disposed on the external side of the small-diameter portion 11a,the welded portion could be finished without permitting weld beads orthe like to protrude to the exterior.

Further, since the small-diameter portion 11a of the half cell 11 wasreinforced by the connecting member 12, the wall thickness of the halfcell 11 could be reduced as a whole. Therefore, the wall thickness ofthe half cell 11 can be reduced and the cooling efficiency of thesuperconducting accelerating tube 10 can be enhanced.

In this case, the superconducting accelerating tube 10 can be freelyformed with a desired length by changing the number of thesuperconducting accelerating tube units shown in FIG. 4.

Further, as schematically shown in FIG. 6, when the half cells 11 andthe connecting members 12 constituting the superconducting acceleratingtube 10 are Formed to have a layer 11c, 12b, respectively of Nb₃ Sn orNbN formed on the internal surface of Nb, it becomes possible that ahigher accelerating electric field can be attained since the criticalmagnetic field is enhanced. The other reference numerals in FIG. 6designate the same elements as described above with reference to FIGS.1-5.

As the design specification of the superconducting accelerating tube ofthis invention, the diameter of the large-diameter portion is set to 80to 90 mm, the diameter of the small-diameter portion is set to approx.10 to 20 mm, and the wall thickness of the material of the half cell 11is set to 0.1 to 1 mm according to the equation (1) expressing therelation between the resonance frequency and the diameter of thelarge-diameter portion in a case where an accelerating tube having aresonance frequency of 3 GHz is used.

In the conventional accelerating tube, the wall thickness of the halfcell must be set equal to or larger than 1 mm, and it will be easilyunderstood that the cooling efficiency of the large-diameter portion isenhanced by use of the superconducting accelerating tube of thisinvention.

Further, when the wall thickness of the half cell 11 is made less than0.1 mm, the mechanical strength of the welded portion of the resultingsuperconducting accelerating tube is lowered so that the wall thicknesscannot be made less than 0.1 mm.

Further, when the resonant frequency is changed, the diameter of thelarge-diameter portion is set to approx. 500 mm according to theequation (1) when an accelerating tube of 500 MHz is used, for example.Therefore, the wall thickness of the half cell i s set to six times thatset in the case of 3 GHz, that is, it is set equal to or more than 0.6mm.

Possibility of Industrial Application

According to a superconducting accelerating tube of this invention, thehalf cells are welded together at the small-diameter portions with thering-shaped connecting members of superconductor disposed therebetweenand therefore the small-diameter portions are reinforced by theconnecting members.

Therefore, according to the superconducting accelerating tube, since theboard thickness of the half cell can be reduced as a whole, time coolingefficiency can be enhanced so that a high accelerating electric fieldcan be obtained with less microwave power, thereby providing advantagesthat the cooling-down cost can be reduced and the area of forinstallation of a cooling device can be reduced.

We claim:
 1. A superconducting accelerating tube comprising:a pluralityof half cells, each half cell being comprised of a superconductormaterial is a dish form and each half cell having a substantiallyconstant thickness; each half cell having a generally circular peripheryand having a small-diameter portion and a large-diameter portion, andwherein each half cell has a shell diameter which varies between thesmall-diameter portion and the large-diameter portion; the respectivelarge-diameter portions of adjacent half cells being connected together;and a respective ring-shaped connecting member, comprised of asuperconductor material, interposed between said small-diameter portionsof adjacent half cells, said adjacent half cells each having a weldedconnection to portions of said ring-shaped connecting members such thatsaid adjacent half cells are connected together via said respectivering-shaped connecting member with said ring-shaped connecting memberdisposed between said small-diameter portions.
 2. The superconductingaccelerating tube of claim 1, wherein said superconductor material ofsaid respective ring-shaped connecting member is Nb.
 3. Thesuperconducting accelerating tube of claim 2, wherein said respectivering-shaped connecting member has a layer of Nb₃ Sn on an internalsurface thereof.
 4. The superconducting accelerating tube of claim 2,wherein said respective ring-shaped connecting member has a layer of NbNon an internal surface thereof.
 5. The superconducting accelerating tubeof claim 1, wherein the material of each of said half cells has athickness in a range between 0.1 mm and 1 mm.
 6. The superconductingaccelerating tube of claim 1, wherein said small-diameter portions ofsaid adjacent cells are connected by the respective welded connection toopposite side portions of said ring-shaped connecting members.
 7. Thesuperconducting accelerating tube of claim 1, wherein saidlarge-diameter portion of adjacent half cells are connected together viaa respective welded connection.
 8. The superconducting accelerating tubeof claim 1, wherein the large-diameter portion of each of said halfcells has an inner diameter, and the material of each of said half cellshas a thickness of not less than 1/800 of the inner diameter of thelarge-diameter portion thereof.
 9. The superconducting accelerating tubeof claim 1, wherein said superconductor material of each of said halfcells is Nb.
 10. The superconducting accelerating tube of claim 9,wherein each of said half cells has a layer of Nb₃ Sn on an internalsurface thereof.
 11. The superconducting accelerating tube of claim 10,wherein the large-diameter portion of each of said half cells has aninner diameter, and the material of each of said half cells has athickness of not less than 1/800 of the inner diameter of thelarge-diameter portion thereof.
 12. The superconducting acceleratingtube of claim 10, wherein said superconductor material of saidrespective ring-shaped connecting member is Nb.
 13. The superconductingaccelerating tube of claim 10, wherein the material of each of said halfcells has a thickness in a range between 0.1 mm and 1 mm.
 14. Thesuperconducting accelerating tube of claim 9, wherein each of said halfcells has a layer of NbN on an internal surface thereof.
 15. Thesuperconducting accelerating tube of claim 14, wherein saidsuperconductor material of said respective ring-shaped connecting memberis Nb.
 16. The superconducting accelerating tube of claim 14, whereinthe large-diameter portion of each of said half cells has an innerdiameter, and the material of each of said half cells has a thickness ofnot less than 1/800 of the inner diameter of the large-diameter portionthereof.
 17. The superconducting accelerating tube of claim 14, whereinthe material of each of said half cells has a thickness in a rangebetween 0.1 mm and 1 mm.
 18. The superconducting accelerating tube ofclaim 9, wherein said superconductor material of said respectivering-shaped connecting member is Nb.
 19. The superconductingaccelerating tube of claim 9, wherein the large-diameter portion of eachof said half cells has an inner diameter, and the material of each ofsaid half cells has a thickness of not less than 1/800 of the innerdiameter of the large-diameter portion thereof.
 20. The superconductingaccelerating tube of claim 9, wherein the material of each of said halfcells has a thickness in a range between 0.1 mm and 1 mm.